After shakedown in the Caribbean, Rowan departed Norfolk on 17 May 1940 for duty in the Pacific, based at San Diego. During the spring of 1941, however, U.S. involvement in the war in Europe increased. In May the limits of the Neutrality Patrol were extended and the Navy gradually expanded its responsibilities for protecting transatlantic convoys.
At the end of the month, Rowan was transferred to the Atlantic and assigned to the Neutrality Patrol. Through the spring and summer, she ranged from Newfoundland to the Caribbean. Then, in early November, she was ordered to escort Convoy WS-12X, carrying British reinforcements for the Near and Far East, from Halifax to Capetown.
Sailing from Halifax on 10 November, she reached Capetown on 9 December, 2 days after the United States entered World War II. In January 1942, she returned to the east coast of the United States and resumed convoy duty in the North Atlantic and the Caribbean. On 30 April she sailed east from Halifax to escort another convoy to the midocean rendezvous point. (continued)